1. Field of the Invention
The present invention relates generally to the field of presbyopic vision correction and, more particularly, to the use of a wavefront sensor for the measurement, design, fit and dispensing of a vision altering optic or vision correcting procedure to improve presbyopic correction and visual performance.
2. Description of Related Art
A form of age-dependent vision deterioration experienced sooner or later by 100% of the population is called presbyopia, i.e., the inability to accommodate or focus on objects close to the eye. Two well-known methods for dealing with presbyopia include alternating vision style correction and simultaneous vision style correction.
In an example of an alternating vision style correction, two (or more/multi-focal) distinct optical regions of a translating style contact lens are designed, one optimized for distance vision and the other for near vision. Typically in an alternating vision bifocal contact lens, the lens will translate on the eye such that the pupil is mostly covered by the distance viewing portion of the lens; however, when eye gaze points downward, such as when a person reads a newspaper, the lens translates on the eye such that the pupil is mostly covered by the near distance viewing portion of the lens.
Alternatively, simultaneous style vision correction has been provided through, e.g., contact lenses, IOLs, refractive surgery, etc. In this style of correction, all light from the object goes through the pupil at the same time, preferably with a 50/50 split between near distance and far distance object light. Any one of a number of refractive or diffractive bifocal or multifocal designs are used to focus light from objects ranging in the field of view from far distance (greater than about 7 m) to near distance (as close as about 25 m but typically about 40 cm) on the retina at the same time.
As a person gets older, not only do they lose the ability to accommodate, they also experience an increase in what are known as higher order wavefront aberrations. These include, but arc not limited to, spherical aberration, coma, irregular astigmatisms (e.g. triangular astigmatism or trefoil), and others. The aberrations corrected by spectacles or single vision contact lenses are limited to defocus and astigmatism which are generally referred to as lower-order aberrations. An increase in spherical aberration brought about, for example, by advancing age, will decrease nighttime vision quality. This may manifest itself as halos or glare around headlights or other light sources. Unfortunately, for the presbyope hoping for better near distance vision with a translating-style contact lens, the correction of the spherical aberration for improved far distance, night time vision results in a decrease in near vision depth of field, i.e., the amount an object""s distance can be shifted before the retinal image of the object has too much blur.
There are also vision tradeoffs for the multifocal, simultaneous style correction lens wearer. Although there are claims of excellent clinical success with a number of simultaneous vision bifocal and multifocal designs, actual published success rates with refractive and diffractive contact lenses for presbyopic correction range only from about 20% to 500% of the general presbyopic population. One of the apparent limiting factors of all current simultaneous style vision correction for presbyopia is lens misalignment; i.e., the lack of control of the centration of the lens relative to the optical axis of the patient. Unfortunately, the induced aberrations caused by the optical misalignment of the eye with the simultaneous vision correction lens reduces visual performance to the point that vision quality is unacceptable to the patient at any viewing distance.
One approach to alleviating vision performance problems is, presumably, to eliminate all optical aberrations in the eye. In the first instance, this solution may not be technically feasible, although correction of wavefront errors via customized refractive surgical techniques and/or customized contact lenses, inlays, onlays, and IOLs, for example, is becoming better understood each day. Moreover, the elimination of all optical aberrations in the eye may not be desirable. For example, reducing spherical aberration will adversely affect depth of field, as discussed above, thus some residual spherical aberration may be desirable for optimum vision quality.
Accordingly, there is a need for vision correcting methods and devices that address the aforementioned problems. In particular, methods and apparatus are needed for providing multifocal lens correction of presbyopia with improvement, or at least no degradation, of other aspects of vision quality.
The invention in general relates to methods and devices for optimizing presbyopic vision correction, preferably with a contact lens, but not limited as such and including, as appropriate, IOLs, inlays, onlays, or refractive surgery. A predominate theme of all of the embodiments of the invention is the use of a wavefront sensor in the design and fitting of alternating vision and simultaneous vision style corrective lenses, or in refractive surgery, and in balancing various aberrations to achieve the best objective vision metric possible.
An embodiment of the invention relates to a method for designing either a customized, multifocal, alternating style translating contact lens or a simultaneous vision style correcting lens, and the providing such a lens to a presbyopic patient. The method comprises the steps of positioning, with respect to a patient""s eye, a multifocal trial lens that is representative of an actual lens to be provided to the patient, wherein the trial lens has a correction of approximately a distance defocus power of the patient""s eye; making a first wavefront aberration measurement of the patient""s eye with the trial lens in position, at a viewing distance equivalent to optical infinity; making a second wavefront aberration measurement of the patient""s eye with the trial lens in position, at an artificial optical near point viewing distance; and using the first and second wavefront aberration measurements to approximate a best form wavefront correction to be applied to the contact lens, whereby the patient""s presbyopic vision is improved. It will be clear to a person skilled in the art that the step of positioning the lens with respect to the patient""s eye has alternative aspects. For example, if the lens to be provided is a translating style, alternating vision type contact lens, the position of the representative trial lens will be on the patient""s eye. In a different aspect where the lens to be provided is a simultaneous vision style correcting lens element, the lens element can be a contact lens that will be positioned on the patient""s eye; however, if the simultaneous vision style correcting lens. element is an IOL, the representative trial lens will be suitably positioned in an optical path of the wavefront sensor device used to make the wavefront aberration measurement. The wavefront aberration measurements are preferably made along a central axis of the trial lens. The best form wavefront correction will provide an optimum retinal image metric, preferably a Point Spread Function (PSF) having a single intensity peak or a Strehl ratio having as large a value as possible, for example. Other retinal image metrics known to those skilled in the art can also be used. The near point viewing distance wavefront measurement should be in the range of about 30-50 cm and will typically be approximately 40 cm. For the case of a translating style, alternating vision type correcting contact lens, the near distance measurement is obtained by inducing a down gaze of the patient""s eye to produce the trial lens translation similar to that of an actual translating multifocal contact lens when worn by the patient. In an aspect of this embodiment, use of the wavefront sensor in designing and fitting a translating style multifocal contact lens will allow the practitioner to monitor the retinal image metric for optimum presbyopic vision while adjusting, e.g., residual spherical aberration in the lens that will result in the best overall vision for the patient while providing an acceptable depth of field to the patient.
In another aspect of the embodiment for designing and providing a simultaneous vision type correcting lens, use of the wavefront sensor facilitates the optimum lateral, vertical, and rotational placement of the lens to optimize the retinal image metric. This can be accomplished, e.g., by adjusting the position of the patient""s head and, therefore, the patient""s optical axis with respect to the measurement axis of the wavefront sensor or, alternatively, utilizing a feedback loop in the wavefront sensor to determine the optimum location in the lens for aberration correction. In a related aspect, wherein a patient has had photorefractive surgery such as LASIK, for example, a retreatment may be performed to correct for misalignment or decentration of the original ablation treatment that resulted in vision degrading higher-order aberrations. Upon retreatment, the surgeon may choose not to fully eliminate the residual spherical aberration.
In another embodiment of the invention, a method for designing a lens or other correction (e.g., refractive surgery correction) to improve a patient""s vision quality that is degraded by both rotationally symmetric and rotationally asymmetric aberrations involves designing the lens or the correction such that a residual amount of the rotationally symmetric aberrations are greater in magnitude than a residual amount of rotationally asymmetric aberrations, e.g., coma. Once again, exemplary metrics for evaluating the patient""s visual quality include, but are not limited to, the PSF and the Strehl ratio. The amount of residual or uncorrected rotationally symmetric aberrations will vary in each patient, and guidance will be provided by the aforementioned metrics. Preferably, the distribution of light in the PSF will not contain multiple peaks.
In another embodiment, a method for designing a lens or a correction for enhancing the near vision performance of a presbyopic patient includes a design that eliminates less than the total amount of the spherical aberration in the person""s visual optical system so as to increase the person""s depth of field. Aspects of this embodiment include ocular corrections that apply to vision altering optics such as contact lenses, IOLs, inlays, onlays, and the like, to the cornea through laser ablation and other refractive surgical techniques, and to other components of the eye.
These and other objects and advantages of the invention will be further apparent in consideration of the drawings and the detailed description of the preferred embodiments, and in view of the appended claims defining the invention.